Little Evidence That Antidepressants Work for Chronic Pain

By Drs. Hollie Birkinshaw and Tamar Pincus

About one in five people globally live with chronic pain, and it is a common reason for seeing a doctor, accounting for one in five GP appointments in the UK.

With growing caution around prescribing opioids – given their potential for addiction – many doctors are looking to prescribe other drugs, “off-label”, to treat long-term pain. A popular option is antidepressants.

In the UK, doctors can prescribe the following antidepressants for “chronic primary pain” (pain without a known underlying cause): amitriptyline, citalopram, duloxetine, fluoxetine, paroxetine and sertraline. Amitriptyline and duloxetine are also recommended for nerve pain, such as sciatica.

However, our review of studies investigating the effectiveness of antidepressants at treating chronic pain found that there is only evidence for one of these drugs: duloxetine.

We found 178 relevant studies with a total of 28,664 participants. It is the largest-ever review of antidepressants for chronic pain and the first to include all antidepressants for all types of chronic pain.

Forty-three of the studies (11,608 people) investigated duloxetine (Cymbalta). We found that it moderately reduces pain and improves mobility. It is the only antidepressant that we are certain has an effect. We also found that a 60mg dose of duloxetine was equally effective in providing pain relief as a 120mg dose.

In comparison, while 43 studies also investigated amitriptyline (Elavil), the total number of participants was only 3,372, indicating that most of these studies are very small and susceptible to biased results.

The number of studies and participants for the other antidepressants are:

• Citalopram (Celexa): five studies with 209 participants

• Fluoxetine (Prozac): 11 studies with 622 participants

• Paroxetine (Paxil): nine studies with 960 participants

• Sertraline (Zoloft): three studies with 210 participants.

The evidence for amitriptyline, citalopram, fluoxetine, paroxetine and sertraline was very poor, and no conclusions could be drawn about their ability to relieve pain.

This is particularly important as UK prescribing data shows 15,784,225 prescriptions of amitriptyline in the last year. It is reasonable to assume that a large proportion of these may be for pain relief because amitriptyline is no longer recommended for treating depression.

This suggests that millions of people may be taking an antidepressant to treat pain even though there is no evidence for its usefulness. In comparison, 3,973,129 duloxetine prescriptions were issued during the same period, for a mixture of depression and pain.

In light of our findings, which were published in May 2023, the UK’s National Institute for Health and Care Excellence (Nice) recently updated its advice to doctors on how to treat chronic pain.

The updated Nice guidance now suggests 60mg of duloxetine to treat [chronic primary pain] and the same drug and dose to treat nerve pain.

Limited Treatments Options

GPs often report frustration at the limited options available to them to treat patients experiencing chronic pain. Amitriptyline is cheap to prescribe – only 66p per pack (US 82.5 cents) – which may explain the high number of prescriptions for this drug.

This is an example of how the gap between evidence and clinical practice could harm patients. Although our review was unable to establish the long-term safety of antidepressant use, previous research has highlighted the high rates of side-effects for amitriptyline, including dizziness, nausea, headaches and constipation.

It’s important to bear in mind, though, that pain is a very individual experience, and the evidence in our review is based on groups of people. We acknowledge that certain drugs may work for people even when the research evidence is inconclusive or unavailable. If you have any concerns about your pain medication, you should discuss this with your doctor.

Hollie Birkinshaw, PhD, is a Research Fellow at University of Southampton. She specializes in research involving chronic musculoskeletal pain, and the integration of psychology in pain and health services. Birkinshaw receives funding from the UK’s National Institute for Health and Care Research (NIHR).

Tamar Pincus, PhD, is a Professor of Health Psychology at University of Southampton. Her research focuses on the psychological aspects of chronic pain. Pincus receives funding from NIHR, Medical Research Council and Versus Arthritis.  

This article originally appeared in The Conversation and is republished with permission.

‘No Reliable Evidence’ That Antidepressants Work for Chronic Pain

By Pat Anson, PNN Editor

Medical guidelines in the United States and United Kingdom may recommend antidepressants for treating chronic pain, but there is “no reliable evidence” that the medications actually work for that purpose, according to a new Cochrane review.

Cochrane reviews are considered the gold standard in medical research because they use robust methodology to gather good quality evidence, while dismissing poor quality research.

A team of UK researchers, led by scientists at the University of Southampton, spent two years examining 176 clinical trials involving nearly 30,000 patients who were prescribed antidepressants for pain. Among the drugs studied were fluoxetine (Prozac), sertraline (Zoloft), amitriptyline (Elavil), milnacipran (Savella), citalopram (Celexa), paroxetine (Paxil) and duloxetine (Cymbalta).

“Our review found no reliable evidence for the long-term efficacy of any antidepressant, and no reliable evidence for their safety for chronic pain at any point. Though we did find that duloxetine provided short-term pain relief for patients we studied, we remain concerned about its possible long-term harm due to the gaps in current evidence,” said lead author Tamar Pincus, PhD, a Psychology Professor at the University of Southampton.

“This is a global public health concern. Chronic pain is a problem for millions who are prescribed antidepressants without sufficient scientific proof they help, nor an understanding of the long-term impact on health.”

In the United States, duloxetine is FDA-approved for fibromyalgia, diabetic neuropathy and musculoskeletal pain. The recently updated CDC guideline recommends that duloxetine and other SNRI antidepressants be used for fibromyalgia and neuropathy, because they provide “small to moderate improvements in chronic pain and function.”

The UK’s National Institute for Health and Care Excellence (NICE) guideline goes even further, stating that antidepressants are better than opioids and other analgesics in treating fibromyalgia, chronic headache, Complex Regional Pain Syndrome (CRPS), musculoskeletal pain and other types of “primary chronic pain” for which there is no known cause.   

The authors of the Cochrane review say regulators in the US and UK should reconsider their recommendations.

“We are calling on governing health bodies NICE and the FDA to update their guidelines to reflect the new scientific evidence, and on funders to stop supporting small and flawed trials. Evidence synthesis is often complex and nuanced but the evidence underpinning the use of these treatments is not equivalent, so current treatment modalities are hard to justify,” said co-author Gavin Stewart, PhD, a statistician at Newcastle University.

Amitriptyline is one of the most commonly prescribed antidepressants for chronic pain in the world. In the last year, around 10 million prescriptions for amitriptyline were given to patients in England for pain, about twice the number prescribed for depression. Many other antidepressants are also prescribed “off-label” for pain, despite limited evidence to support their use.

“Though previous investigations show that some antidepressants might relieve pain, there has never been a comprehensive study examining all medications across all chronic conditions – until now,” said co-author Hollie Birkinshaw, PhD, a Research Associate at the University of Southampton.

“The only reliable evidence is for duloxetine. Adopting a person-centered approach is critical to treatment and, when patients and clinicians decide together to try antidepressants, they should start from the drug for which there is good evidence.”

The reviewers say duloxetine was the highest-rated antidepressant for treating fibromyalgia, musculoskeletal and neuropathic pain. Standard doses of duloxetine were just as effective as higher ones. Milnacipran was also effective at reducing pain, although the evidence was weaker.

“We simply cannot tell about other antidepressants because sufficiently good studies are not available – but it does not mean that people should stop taking prescribed medication without consulting their GP,” said Pincus.

A common complaint of patients who take duloxetine is that it makes them dizzy and nauseous. Many quickly become dependent on the drug and then have severe withdrawal symptoms when they stop taking it.

Several previous studies have also raised questions about using antidepressants for pain. A recent review of over two dozen clinical trials by Australian researchers found little evidence to support the use of antidepressants in pain management. Nearly half of the trials had ties or funding from the pharmaceutical industry.